The present invention relates to a mobile communication system, a network and a mobile station, for performing a radio communication in a radio zone. Particularly, it relates to a mobile communication system, a network and a mobile station, capable of switching a radio zone or a channel(i.e. handover) at a high speed.
Generally, in a mobile communication system, a base station selects a single radio zone and a single radio channel and notifies a mobile station of the selected radio zone and radio channel when the mobile station switches a radio zone. Thereafter, the mobile station switches the channel to the notified radio channel.
Incidentally, in a handover control procedure of a radio channel, a handover to the notified radio channel is sometimes impossible to be performed due to effect of interference, etc. In such a case, it is necessary for the mobile station to receive a notice of a candidate radio zone and a candidate radio channel once again from the same base station. That is, in case a handover procedure of a radio zone results in failure, the mobile station must receive a notice of another candidate again from the base station each time a handover procedure results in failure, until a handover procedure is performed successfully. For those reasons, the procedure for switching a channel is sometimes delayed in the conventional mobile communication system.
Also, in a PDC (Personal Digital Cellular) type mobile communication system which is now commercially served in Japan, a base station periodically notifies a mobile station of a representative channel of a common control channel for peripheral zones. Upon receipt of a notice, the mobile station switches the channel to the representative channel of the handover target zone first. Then, the mobile station obtains information on channels usable in the handover target zone, through the representative channel. Thereafter, the mobile station switches the channel within the target zone.
As discussed above, in the PDC type common control channel, the mobile station must perform a channel handover procedure twice; the first is a channel handover to a representative channel so that a radio zone handover can be performed through the representative channel and the second is a channel handover to be performed within the handover target radio zone. For those reasons, in the conventional mobile communication system, a long time is required for performing the channel handover procedure consisting of a radio zone handover procedure and a channel handover procedure to be performed within that radio zone. On the other hand, another approach may be possible in which a base station notifies a mobile station of all channels for peripheral zones and the mobile station selects a specific channel among all channels notified so that the mobile station can switch the channel directly to the selected channel. However, this is not preferred because when the base station notifies the mobile station of all channels for the peripheral zones, the traffic of down channel from the base station to the mobile station is increased.